The invention relates to a method and apparatus for correcting the thickness profile of the strip to be rolled in a multiple-stand hot strip mill train.
Several devices are known with which the shape of the roll gap and thus the thickness profile of the strip to be rolled can be changed. There are roll stands where the upper roll can be swung somewhat so that a small rotation occurs around an imaginary axis extending horizontally through the center of the roll and lying 90.degree. relative to the roll axis. Such a device is used for plane level controlling.
Devices are also known with which the shape of the roll is somewhat changed in that the roll or its bearings are somewhat bent opposite the roll setting means by hydraulic means at both ends. This bending is necessary at the edges because the roll would otherwise roll the strip flatter at the edges than in the middle, since the edges have a stronger flow under roll pressure than the center of the strip.
These two known correcting devices have been used up to now for making rough adjustments for faults which arose due to wear and whose extent was indicated periodically at the finished, rolled strip by conventional measuring methods.
Changes with faster effect were only possible so far in case of a non-plane strip, e.g. when the strip forms waves at one side. This was immediately visible to the operating personnel. The wave shape at one side always comes about when this side has been rolled too strongly. In this case the sheet becomes longer and forms waves. In case of wave forming, the operator had to increase the roll gap at one of the roll stands by pivoting one roll at the side where the wave shape forms.
This regulation of a one-sided wave shape can be carried out automatically and very fast by installing a measuring device for measuring the roll tensions distributed over the width of the band, as is known from U.S. Pat. No. 4,116,029.
With these known methods and means for correcting the shape of the roll gap, only rough irregularities can be removed, because the center line of the strip does not always correspond with the center of the mill train and the strip constantly changes its position obliquely to the center line of the roll train. Sometimes the fluctuations are so great that the strip runs laterally against the limits of the roll train which badly interrupts the manufacturing process.
It is an object of the invention to reduce considerably the lateral, oblique fluctuations of the strip which occur in the direction of movement of the strip and to provide fast-acting, exact correction possibilities of the thickness profile by changing the roll gap.